Photochemistry of cyclic trisilanes: "spring-loaded" precursors to methylphenylsilylene.

Two new cyclic trisilanes containing a SiMePh moiety in the central position have been synthesized, and their photochemistries studied by steady-state and laser flash photolysis methods. The yield of the transient silylene SiMePh increases at the expense of that of the corresponding cyclic silene derivative (formed by photochemical 1,3-silyl migration into the phenyl ring) as the ring size is decreased from 7 to 6, facilitating the direct detection of the silylene by laser flash photolysis. The UV/Vis spectrum of SiMePh in hexanes solution (lambda(max)=270, 505 nm) and absolute rate constants for its reaction with methanol, triethylsilane, a terminal alkene, alkyne, and two aliphatic dienes at 25 degrees C are reported.